#include <bits/stdc++.h>
#define rep(i, a) for (int i = 0; i < (a); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define repr(i, a) for (int i = (a) - 1; i >= 0; i--)
#define repr2(i, a, b) for (int i = (b) - 1; i >= (a); i--)
using namespace std;
typedef long long ll;
const ll inf = 1e9;
const ll mod = 1e9 + 7;

int N, A[100];

int main() {
	cin >> N;
	rep (i, N) cin >> A[i];

	int ans = 0;
	rep (i, N - 2) {
		if (A[i] == A[i + 1]) continue;
		if (A[i] == A[i + 2]) continue;
		if (A[i + 1] == A[i + 2]) continue;

		if (A[i] < A[i + 1] && A[i + 1] > A[i + 2]) {
			ans++;
		}
		if (A[i] > A[i + 1] && A[i + 1] < A[i + 2]) {
			ans++;
		}
	}
	cout << ans << endl;

	return 0;
}